This disclosure is related to pre-emphasis driver control for electrical signal interconnects within a computing platform.
As data transmission rates increase between components within computing platforms and/or other electronic devices, signal integrity issues become more important. One example of a potential signal integrity issue is Inter-Symbol Interference (ISI). ISI may be the result of one or more potential causes of signal degradation. One potential cause may be the attenuation and/or the dispersal of frequency components that may result from signal propagation down a transmission line, for example propagation along a signal trace on a printed circuit board. Another potential cause of ISI may be un-matched termination capacitance and/or relatively heavy capacitive loading at a receiving device. For example, graphics processing devices may interface with memory modules that may comprise a number of memory components, and each of the memory components may add to the capacitive loading on the graphics memory interface. Still another cause may be the potential variations in rise and fall times that may follow varying sequences of ones and zeros (logically high voltage levels and logically low voltage levels, respectively) being driven onto a transmission line. This issue may be referred to as pattern-dependent ISI.
FIG. 1 is a diagram that depicts an example of the potential effects of the issues discussed above. A driver input signal 101 for this example may represent a data signal generated by a logic unit within an integrated circuit device. The data signal may be presented at an input of a driver circuit, and the driver circuit may generate a driver output signal 103. The driver output signal may be coupled to a receiving device via a data interconnect, perhaps a signal trace on a printed circuit board. Because of the characteristics of the driver circuit, the data interconnect, and/or the receiving device (such characteristics may include impedance and/or capacitance and/or other characteristics), the data pulse on driver output signal 103 may differ from the data pulse presented at the driver circuit input 101. As depicted in FIG. 1, the output data pulse on driver output 103 may respond to the aforementioned characteristics with a loss of amplitude, displacement in time, rounded edges, and/or a “smearing” of the pulse into adjacent time slots or unit intervals (perhaps referred to as “bit-times”). At time 110 for this example, the receiving device may sample the value on the driver output signal. One bit-time later, at time 120, the receiving device may again sample the value on driver output signal 103. Because in this example the voltage on driver output 103 has not yet fallen to a logically low voltage level, the value on driver output 103 may be misinterpreted. This smearing of data values into adjacent bit-times is an example of ISI. ISI may result in increased transmission error rates, particularly as data transmission rates increase, thereby limiting data transmission rates and overall computing platform performance.